<template>
  <div class="pagination">
    <button :disabled="pageNo == 1"
            @click="$emit('getPageNo', pageNo - 1)">上一页</button>
    <button v-if="startNumandendNum.start > 1"
            @click="$emit('getPageNo', 1)"
            :class="{active:pageNo == 1}">1</button>
    <button v-if="startNumandendNum.start > 2">···</button>

    <!-- 中间部分 -->
    <button v-for="(page, index) in startNumandendNum.end"
            :key="index"
            v-if="page >= startNumandendNum.start"
            @click="$emit('getPageNo',page)"
            :class="{active:pageNo == page}">{{page}}</button>

    <button v-if="startNumandendNum.end < totalPage - 1">···</button>
    <button v-if="startNumandendNum.end < totalPage"
            @click="$emit('getPageNo',totalPage)"
            :class="{active:pageNo == totalPage}">{{totalPage}}</button>
    <button :disabled="pageNo == totalPage"
            @click="$emit('getPageNo', pageNo + 1)">下一页</button>

    <button style="margin-left: 30px">共 {{total}} 条</button>
  </div>
</template>

<script>
export default {
  name: "Pagination",
  props: ['pageNo', 'pageSize', 'total', 'continues'],
  computed: {
    // 总共多少页
    totalPage() {
      // 向上取整
      return Math.ceil(this.total / this.pageSize)
    },
    // 计算出连续的页码的起始数字和结束数字
    startNumandendNum() {
      const { continues, pageNo, totalPage } = this
      // 先定义两个变量存放开始数字和结束数字
      let start = 0, end = 0
      // 连续页码数字5【就是至少5】，如果出现不正常的现象【就是不够5页】
      // 不正常现象【总页数没有连续页码多】
      if (continues > totalPage) {
        start = 1
        end = totalPage
      } else {
        // 正常现象【连续页码5，但是总页数一定大于5】
        start = pageNo - parseInt(continues / 2)
        end = pageNo + parseInt(continues / 2)

        // start会出现【0|负数】的现象 ---纠正
        if (start < 1) {
          start = 1
          end = continues
        }

        // end会出现大于【总页数totalPage】的现象 ---纠正
        if (end > totalPage) {
          end = totalPage
          start = totalPage - continues + 1
        }
      }
      return { start, end }
    }
  }
}
</script>

<style lang="less" scoped>
.pagination {
  text-align: center;
  button {
    margin: 0 5px;
    background-color: #f4f4f5;
    color: #606266;
    outline: none;
    border-radius: 2px;
    padding: 0 4px;
    vertical-align: top;
    display: inline-block;
    font-size: 13px;
    min-width: 35.5px;
    height: 28px;
    line-height: 28px;
    cursor: pointer;
    box-sizing: border-box;
    text-align: center;
    border: 0;

    &[disabled] {
      color: #c0c4cc;
      cursor: not-allowed;
    }

    &.active {
      cursor: not-allowed;
      background-color: #409eff;
      color: #fff;
    }
  }
}
</style>
